Across
- 2. Second planet from the sun and similar in size to Earth
- 5. Smallest planet in our solar system
- 7. The time it takes a planet to complete an orbit around the sun
- 8. The time it takes a planet to complete one full spin on its axis (one "day" on that planet)
- 10. Called the "Red Planet" (iron oxide)
- 13. Vertical axis on HR diagram
- 14. Cooler stars burn this color
Down
- 1. Cloud of gas and dust where stars and planets form
- 3. Massive ball of hot gases that emits light and heat through nuclear fusion
- 4. Horizontal axis on HR diagram
- 6. Allows astronomers to classify stars and understand their life cycles
- 9. Atmosphere: nitrogen (78%), oxygen (21%)
- 11. The star at the center of our solar system
- 12. Hotter stars burn this color